This invention relates to coal piping for delivering pulverized coal to a steam generator, and in particular to an orifice for modifying the flow distribution between parallel lines.
Pulverized coal is conventionally entrained in air at the pulverizer and delivered through fuel pipes to a steam generator. A plurality of fuel pipes in parallel flow relationship are used to convey this coal. Maldistribution of flow through the pipes has a detrimental effect on furnace performance. Also should the flow because of this maldistribution become too low in a particular pipe, the coal will drop out of suspension and plugging of the line will occur. This low flow in any one line is normally the result of an excessive flow in other lines.
Since the pulverized coal lines must travel various routes and distances from the pulverizer to the particular location of entry into the furnace, a maldistribution of flow inherently occurs. It has been conventional practice to modify this distribution so as to obtain uniform flows by inserting orifices within the flow lines.
The pulverized coal clearly has a severe erosive effect. Orifices are initially installed to obtain the proper distribution. They erode during operation, and when decreased performance of the furnace or plugging of the coal lines is noticed, the orifices must be replaced. It has been present practice to use hardened materials such as Ni-hard or surface hardening of the orifice plate. While this increases the life of the orifice beyond that of cast iron or normal steel, it still requires frequent replacement of the orifices.
The straight replacement of a ceramic for steel cannot readily be made because of the difficulty and expense of forming a sufficiently dense annular member of ceramic material and because of the potential that exists for erratic cracking of the ceramic material due to physical bending of the pipe or thermal changes thereof during operation.